Ceramic cutting tools have gained public favor since their development because they are capable of cutting iron or steel at high speed and have excellent abrasion resistance, compared to conventional cutting tools. However, the market share of ceramic cutting tools is only about 5% of the total due to their inherent vulnerability. Therefore, overcoming this vulnerability remains to be solved.
A cutting tool made of Al.sub.2 O.sub.3 -TiC system has recently been getting public favor by overcoming the former deficiency of toughness and because of the decrease of rust. However, since such cutting tools of the Al.sub.2 O.sub.3 -TiC system are made from a material which is difficult to be sintered if it is not at a high temperature, and there are many problems including the high cost of production and the complexity of processing.
Though many studies for producing a dense sintered body of the Al.sub.2 O.sub.3 -TiC system have been made, it is difficult to produce a perfectly dense sintered body because TiC is difficult to be sintered compared to Al.sub.2 O.sub.3 and the mechanical characteristics of the sintered body decreases because gases such as Al.sub.2 O.sub.3 or O.sub.2 are generated at the interface between Al.sub.2 O.sub.3 and TiC during the sintering reaction to form pores in the sintered body.
Because of the difficulty in sintering, methods such as using HIP(Hot Isostatic Pressing After Sintering), by Hot-Pressing, by sintering quickly, raising the temperature to 1800.degree. C. or more, or by adding sintering assistants such as Y.sub.2 O.sub.3 and etc. have conventionally been used.
However, the method by Hot-Pressing provides a difficulty in diversifying the shape of the sintered body because only one sintered body is produced by pressing and therefore is not proper for mass production. Also, since the temperature is suddenly raised to a high temperature, the sintered body suffers from thermal shock. As a result, the transformation or the breaking of the sintered body occurs. Moreover, it is very difficult to obtain a dense sintered body because of the bending of the body by unequal heating and volatilization on the surface of the sintered body.
To overcome such problems, several methods have been proposed.
For example, Japanese Patent Publication Sho. 49-1444 discloses a method comprising the addition of sintering assistants such as NiO and MgO to the main material of sintered body in order to prevent the decrease of strength by inhibiting the growth of Al.sub.2 O.sub.3 particles and by improving the bond intensity of Al.sub.2 O.sub.3 and TiC. Japanese Patent Publication Sho. 56-140066 discloses a method comprising the addition of sintering assistants such as MgO, NiO, or Cr.sub.2 O.sub.3 to obtain a dense sintered body. However, said methods induce the growth of Al.sub.2 O.sub.3 crystals which decrease the characteristics required for a cutting tool such as mechanical strength and toughness.
On the other hand, Japanese Patent Publication Sho. 51-569, Sho. 62-45194, Sho. 64-1430 and Japanese Patent Laid-Open Publication Sho. 54-104407 disclose methods comprising the addition of TiO.sub.2 powder as a sintering assistant to obtain a dense sintered body. Though the bond intensity and the wettability are improved by this method, the sintered body is easily broken by thermal shock resulting from high-speed cutting because TiO.sub.2, TiC and TiCO are not homogeneously mixed inside the sintered body.